Historically, pavement markings have fallen into three basic classes:
(1) Painted lines having glass spheres embedded in a polymeric material to provide some degree of retroreflection;
(2) Preformed tapes comprised of polymeric film having an adhesive on one side and a layer of glass spheres on the other; and
(3) Raised pavement markers providing discrete points of a retroreflective material.
Raised pavement markers offer a greater degree of night delineation or retroreflection, wet or dry, than is offered by painted lines and tapes. Most commercial forms of raised lane delineators comprise a flat-bottomed disk or base (ceramic, polymeric or metal) having a raised portion which carries a reflector portion made of reflective glass microspheres or cube-corner reflector inserts. After the passage of time, these devices can move or slide out of position under the repeated impact of vehicle wheels.
Raised markers or delineators have found wide application in road markings, but their application would be even wider except for some disadvantages, specifically: cost (more expensive than tape or reflective paint), poor durability (broken upon impact, scratched, etc.) and placement, requiring curing glues (epoxy), holes or anchors to remain in place. In geographic areas in which roadways must be plowed to clear them of snow, such lane delineators are removed by the plowing operation. Furthermore, raised markers made of a hard or heavy material could cause property damage and injury if they were thrown into the air by a snowplow, e.g., breaking a passing motorist's windshield.
Some known pavement markers have a raised rubber reflecting portion or tab which is intended to bend over under a vehicle tire. Others have a reflecting portion which is supposed to retract into a recess in the pavement. The former type is illustrated by U.S. Pat. Nos. 4,111,581; 3,963,362; 3,879,148; and 3,785,719. In all of these patents, the reflecting portion is a flat reflectorized rubber piece or tab rising above the pavement surface. The tab is supported at its bottom by attachment to the base portion. These designs suffer from at least two disadvantages: a. fatigue at the joint between the reflecting tab and the base (causing the tab to fail to recover to its intended position or to simply lie flat); and b. creasing or breaking of the reflector due to the flexing of the tab at some point inbetween its top and the base. The forces exerted by a moving vehicle tire on a pavement marker are complex and change as the tire traverses the marker. Vertical tab markers actually tend to crimp or bend in the middle before bending near the base.
Markers having reflecting surface tabs oriented at an obtuse angle to the road surface, tend to lose reflectivity rapidly due to the action of dirt and grit as tires pass over the reflector.
The object of this invention is a raised pavement marker offering a high degree of reflectivity which is retained for a long time, low cost, ease of placement, improved durability, and safety while alleviating the support and creasing problems of prior raised rubber markers.